If you’re receiving Mail Delivery Failure notices for messages you are sure you did not send, there may be two causes:
1. Your computer has been infected by a virus that is sending emails from your address without your knowledge.
2. A spammer is forging your email address for the spam they’re generating. Email addresses are forged in order to disguise the actual origin of the message. In almost all cases of forgery, the message is sent from a different location and not from your email account and/or email service.
In both these cases, the messages are sent to random email addresses, that are placed in the To:, Cc:, or Bcc: fields. If the recipient email address happens to be valid, they’ll receive the spam/ email fraud. However, if the recipient email address is invalid, you’ll receive a Mail Delivery Failure notification.
If you receive a Mail Deliver Failure notice but have not sent any messages, please take the following steps to check your computer:
1. Change your account password to something more secure. Use a password that is easy for you to remember but difficult for other people to guess. Avoid using birthdays or children’s names, and instead, think of a line from an old movie or song and use the first letter of each word. Use both letter and number combinations with at least 6 characters.
2. Run a Virus Scan and remove any infections. Make sure that you have installed the latest updates for your anti-virus program, then run a complete system scan to identify and remove any virus or malicious program. If you currently don’t have an anti-virus program installed in your system or if your subscription for regular updates has already expired,
Credit to original Post by; https://help.netzero.net/nzhelp/support-home-page/service-help/online-security/security-tips/mail-delivery-notice-for-a-message-i-did-not-send/
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